1. Field of the Invention
This invention relates to a ventilator system for controlling, assisting and monitoring a patient's breathing and more particularly concerns improvements in the ventilator system described in my prior U.S. Pat. No. 4,141,354. The improvements are especially concerned with a novel pneumatic PEEP/ASSIST circuit and with an improved pneumatic circuit for limiting the breathing gas pressure directed to a patient using the system.
2. Description of the Prior Art
In my prior U.S. Pat. No. 4,141,354, two separate pneumatic circuits were provided to permit the operator of the ventilator system to use the system as a breathing controller, with or without PEEP, or as an assistor-controller. When the prior system was used as a breathing assistor-controller, there was no convenient provision for also employing PEEP in an assist compensated mode. For example, if the ASSIST setting was established at a given value, say -2 cmH.sub.2 O, and at PEEP settings of 10 and 15 cmH.sub.2 O, the inspiratory efforts which would be the sum of the PEEP setting and the ASSIST setting cannot be obtained by the patient.
The ventilatory system described in my abovementioned prior patent, employed a spring loaded safety valve to dump breathing gas when pressure in the patient breathing circuit exceeded a preset magnitude determined by the spring bias in the valve. This type of valve is always characterized by throttling during its operation. When the pressure in the patient breathing circuit exceeds the preset magnitude of the spring bias, the valve theoretically opens to dump gas to prevent a pressure rise above the preset magnitude. In practice, due to the throttling characteristic of the valve, a retard occurs in the dumping action, so that the pressure in the patient's breathing circuit can greatly exceed the preset magnitude or value desired, particularly at high inspiratory flow rates, when the dumping action cannot keep up with the introduction of breathing gas into the breathing circuit.